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  • 1
    Publication Date: 2018-12-01
    Description: The initiation of the breakdown process for axially symmetric compressible flows is investigated using a numerical solution of the conservation equations for mass, momentum, and energy. The vortex is isolated, with its axis parallel to the direction of the main stream, and the core radius is small compared to the breakdown length. Computations for several flowfields indicate that the breakdown of the solution is shifted further downstream with increasing Mach number until breakdown is no longer observed. In the subsonic case, the influence of the initial temperature distribution on the breakdown length of the solution is more pronounced than in the supersonic case, with heating of the core enhancing breakdown, and cooling delaying it. The breakdown of the solution is seen to always occur for nonvanishing axial velocity components.
    Keywords: AERODYNAMICS
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  • 2
    Publication Date: 2018-12-01
    Description: The onset of vortex breakdown in compressible flows is investigated analytically for the case in which the flow is axially symmetric, the vortex is isolated, its axis is parallel to the main flow, and the vortex radius is small compared to the breakdown length. The conservation equations for mass, momentum, and energy are formulated and solved numerically using a finite-difference scheme, as described by Krause (1985); numerical results are presented in graphs and briefly characterized.
    Keywords: AERODYNAMICS
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  • 3
    Publication Date: 2019-07-13
    Description: The slender-vortex approximation was analyzed for incompressible and compressible flow. First the equations of motion were reduced in an order of magnitude analysis. Then compatibility conditions were formulated for the inflow conditions. Thereafter finite-difference-solutions were constructed for incompressible and compressible flow. Finally it was shown that these solutions can be used to describe the flow in slender vortices. The analysis of the breakdown process must, however, be excluded, since its upstream influence cannot be predicted with the slender vortex approximation. The investigaton of this problem is left for future work.
    Keywords: AERODYNAMICS
    Type: NASA-CR-176853 , NAS 1.26:176853
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  • 4
    Publication Date: 2019-07-12
    Description: The subject has been jointly investigated at NASA Langley Research Center and the Aerodynamisches Institut of the RWTH Aachen over a substantial period. The aim of this investigation has been to develop numerical integration procedures for the Navier-Stokes equations - particularly for incompressible three-dimensional viscous flows about simple and double delta wings - and to study the low speed flow behavior, with its complex vortex structures on the leeward side of the wing. The low speed flight regime poses unusual problems because high incidence flight conditions may, for example, encounter symmetric and asymmetric vortex breakdown. Because of the many difficulties to be expected in solving the problem, it was divided into two - analysis of the flow without vortex breakdown and analysis of the breakdown of isolated vortices. The major results obtained so far on the two topics are briefly described.
    Keywords: AERODYNAMICS
    Type: Zeitschrift fuer Flugwissenschaften und Weltraumforschung (ISSN 0342-068X); 13; 291-301
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